Throughout this application, various patents are referred to by an identifying citation. The disclosures of the patents referenced in this application are hereby incorporated by reference into the present disclosure to more fully describe the state of the art to which this invention pertains.
Lithium batteries are widely used in portable electronics, such as smartphones and portable computers. Among the new applications for lithium batteries are high power batteries for hybrid, plug-in hybrid, and electric vehicles. However, broad acceptance of electric vehicles requires batteries that can be constructed at lower cost and that include improved safety features.
Existing processes for manufacturing lithium batteries, including rechargeable and non-rechargeable lithium batteries, and other types of batteries, are relatively slow, complex and expensive. For example, rechargeable lithium-ion batteries are typically constructed by interleaving strips of the various layers of the battery to form a stack. These layers may include a plastic separator, a conductive metal substrate with a cathode layer coated on both sides, another plastic separator, and another conductive metal substrate with an anode layer coated on both sides. This interleaving is usually done on manufacturing equipment that is inefficient and costly to construct and operate. Thus, there is a need for manufacturing techniques that do not require interleaving discrete battery layers.
As noted above, current lithium batteries are fabricated using metal substrates. During manufacture, these metal substrates are typically slit into discrete battery stacks. This has been known to result in metal fragments being embedded into the separator or other portion of the finished battery, which can lead to a short circuit, or other dangerous condition. Thus, there is a need for improved manufacturing techniques that eliminate these safety concerns.
In addition, one of the known challenges in reducing the cost of lithium-ion batteries is the composition of the cathode. In this regard, the cathode material often comprises thirty percent, or more, of the total battery cost. Thus, there has been increased interest in utilizing manganese and its oxides as a cathode material because manganese is considerably less expensive than other cathode materials and is found in abundance in nature. However, when used as a cathode in lithium-ion batteries, manganese is easily dissolved, particularly at higher temperatures. During operation, the dissolved manganese ions are deposited on the separator and anode resulting in reduced battery cycle life. Moreover, this migration problem is not limited to manganese. In this regard, there has also been a shift in the battery industry to cathodes comprising nickel-manganese-cobalt oxide (NMC) and, in particular, nickel-rich NMC. However, nickel and cobalt ions, like manganese ions, diffuse through the separator and onto the anode, reducing battery cycle life. Thus, it would be advantageous if the migration of these metals (e.g. manganese, nickel and cobalt) could be controlled and eliminated.